1. Field of the Invention
The present invention relates to minienvironments in which semiconductor wafers may be processed, and in particular to an integrated system for monitoring and controlling all minienvironment functions and parameters.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an enclosed space, or minienvironment, located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassette between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (xcexcm) to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half xcexcm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with 1 xcexcm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
In order to transfer wafers and/or a wafer cassette from within the SMIF pod to within a minienvironment on a processing tool, a door of the pod is supported on an I/O port of the minienvironment. The pod is designed so that the pod door overlies a port door covering the I/O port of the minienvironment, and the pod cover overlies a port plate surrounding the port door. Once located at the I/O port, mechanisms within the port door release and separate the pod door from the pod cover. Thereafter, the port door and pod door are brought into the I/O minienvironment, and moved together either up, down, or to the side of the minienvironment port to clear a path for the wafers and/or cassette to be transferred through the port. While the port and pod doors are retracted within the minienvironment, the pod cover generally remains affixed to the I/O port to prevent contaminants from entering the minienvironment.
It is extremely expensive to maintain cleanroom conditions, and it would be desirable not to have to provide clean air exterior to the minienvironments inside the fab. However, where the air surrounding a minienvironment includes large numbers of a particulates per unit volume, it becomes more difficult to maintain conditions within the minienvironment at the desired cleanroom level. At present, it is desirable to maintain a better than class 1 cleanroom environment within a minienvironment, while allowing the ambient conditions within the fab to be about class 1000 and as high as class 100,000. Such disparate cleanroom conditions inside and outside the minienvironment put strict requirements on the differential pressure control system associated with a minienvironment to ensure that the ambient particulates do not enter the minienvironment.
In addition to differential pressure, it is critical to closely monitor and control other environmental conditions within the minienvironment, such as for example the particle count, temperature and humidity. Particle Measuring Systems, Inc. of Boulder, Colo. provides a software package entitled xe2x80x9cFacility-Viewxe2x80x9d which allows an operator to collect, display and analyze data pertaining to certain cleanroom environmental conditions, such as for example pressure, temperature, and particle count. Another cleanroom monitoring system is available from Lighthouse Associates of Milpitas, Calif. The Lighthouse monitoring system is also capable of monitoring certain cleanroom conditions, such as for example pressure, temperature, relative humidity, and particle count and then presenting real-time data in a variety of formats including graphs, charts, data tables and maps.
Up until now, no cleanroom monitoring system has offered fully integrated monitoring and control of all parameters within each minienvironment on a tool and fab-wide basis. While it is known to monitor a variety of parameters, each of those parameters are conventionally monitored by a separate controller and/or a separate network connection to a host system. Moreover, conventional cleanroom monitoring systems have not allowed expansion of the system once the system is in place within a cleanroom.
It is therefore an advantage of the present invention to provide a fully integrated minienvironment control and monitoring system on both a tool and fab-wide level.
It is a further advantage of the present invention to provide an integrated system providing a comprehensive monitoring and control of all functions and parameters within a minienvironment.
It is another advantage of the present invention to provide a single controller, having a single network connection, for controlling and monitoring all environmental conditions within a minienvironment.
It is a further advantage of the present invention to connect all minienvironments within a fab into a local area network to allow communication between the minienvironments and a host system, and to allow remote monitoring and control of each minienvironment.
It is another advantage of the present invention to provide an integrated communication link with choice of standard protocols to allow integration of minienvironment control with other equipment control and automation systems.
It is a still further advantage of the present invention to provide an automatic protection and early warning system for equipment to reduce downtime and equipment maintenance.
It is a further advantage of the present invention to provide a system for collecting and preserving historical data from each minienvironment for minienvironment quality verification and for problem identification.
It is yet another advantage of the present invention to provide a disaster control and prevention system through early detection and immediate response to hazardous conditions such as smoke, fire, or chemical spill.
These and other advantages are provided by embodiments of the present invention which in general relate to an intelligent minienvironment control system. The system is designed to optimize the minienvironment performance, improve the protection for the multi-million dollar equipment within a fab, and to improve the safety conditions for fab personnel. The intelligent minienvironment control system is comprised of a plurality of minienvironment control and monitoring systems (MCMSs), one such system being associated with each minienvironment in the fab. The MCMSs continuously monitor environmental conditions within the minienvironments relating for example to differential pressure, airborne particulate level, temperature, humidity and smoke. Should any of the environmental parameters deviate from their predetermined and preset values, the parameter is quickly corrected and/or other appropriate action taken. For example, the smoke sensors are provided both within and outside of a minienvironment. If smoke is detected within or around a minienvironment, the associated MCMS automatically sounds an alarm, shuts down the air circulation system within the minienvironment to minimize the possibility of contaminating the equipment, and/or activates a sprinkler system within the minienvironment
Each of the MCMSs are linked together as part of a local area network forming an integrated fab-wide minienvironment management system. The system utilizes IP/IPX protocols and allows any computer supporting IPX protocols to communicate with the MCMSs. The management system also includes workstations linked to the network for storing historical data for, and allowing remote access to, each of the MCMSs in the system.